1. Field
This disclosure generally relates to the fabrication of composite parts, and deals more particularly with a method and apparatus for forming stiffeners, such as aircraft fuselage stringers.
2. Background
Composite parts, such as stiffeners used in the aircraft industry, may be fabricated in a multi-step process in which separate tooling is used for laying up, forming-to-shape, and curing a multi-ply composite charge. The composite charge may assembled by sequentially laying up individual plies according to a predetermined ply schedule, either by hand or using automated equipment, on a layup tool or other substrate. During this initial layup process, the layup tool may include features that preform the charge. The preformed charge is then transferred to a male or female mold in a press former where the preformed charge is formed to final shape. The formed charge is then transferred to an IML (inner mold line) cure tool where it is cured in an autoclave or an oven.
The need for separate tools for laying up and curing of composite parts adds to production flow times, material and/or labor costs, and may contribute to undesirable tolerance location buildup. Additionally, the use of separate tools for layup and cure introduces the potential for the part layup to change shape and/or wrinkle caused by transportation and/or relaxation from dwell times at pre-installation stages.
In addition to the problems discussed above, existing press forming equipment used to form composite charges to final shape may allow the composite charge to shift out of position during the forming process as the charge is compressed between male and female tool dies. When the charge shifts out of position during forming, the finished part may be out of tolerance or mis-shaped, causing the part to be scrapped.
Accordingly, there is a need for a method and apparatus for forming a composite part, such as a stiffener, in-place in a cure tool, thus eliminating the need for layup or forming tools. There is also a need for a method and apparatus of the type mentioned above which controls the centerline position of the composite charge as it is being formed on the cure tool.